Through the advent of modern medicine, numerous diseases may now be treated with a wide variety of pharmaceuticals. Nevertheless, infectious diseases are a serious concern in developing countries, in immunocompromised individuals, and for certain diseases where no adequate treatment exists.
In developing countries, poor hygeine and a lack of adequate sanitation provide an environment which promotes infectious diseases. Even in countries with adequate sanitation, a constant onslaught of infectious agents may stress the immune system defenses to subnormal levels, thus permitting the development of disease.
Although vaccines are available to protect against some of these diseases, vaccinations are not always feasible due to factors such as delivery too late in the infection or inability of the patient to mount an immune response to the vaccine. One such disease is hepatitis, which is a systemic disease that predominantly affects the liver. Briefly, this disease is typified by the initial onset of symptoms such as anorexia, nausea, vomiting, fatigue, malaise, arthraigias, myalgias, and headaches, followed by the onset of jaundice. The disease may also be characterized by increased serum levels of the aminotransferases AST and ALT. Quantification of these enzymes in serum indicates the extent of liver damage.
There are five general categories of viral agents which have been associated with hepatitis: the hepatitis A virus (HAV); the hepatitis B virus (HBV). two types of non-A, non-B (NANB) agents, one blood-borne (hepatitis C) and the other enterically transmitted (hepatitis E); and the HBV-associated delta agent (hepatitis D).
There are two general clinical categories of hepatitis, acute hepatitis and chronic hepatitis. Symptoms for acute hepatitis range from asymptomatic and non-apparent to fatal infections. The disease may be subclinical and persistent, or rapidly progress to chronic liver disease with cirrhosis, and in some cases, to hepatocellular carcinoma. Acute hepatitis B infection in adult Caucasians in the United States progresses to chronic hepatitis B in about 5% to 10% of the cases. In the remainder of the cases, approximately 65% are asymptomatic. In the Far East, infection is usually perinatal, and 50% to 90% progress to the chronic state. It is likely that the different rates of progression are linked to the age at infection rather than genetic differences in the hosts. In the United States, about 0.2% of the population is chronically infected, with higher percentages in high-risk groups such as physicians, drug addicts and renal dialysis patients. In countries such as Taiwan, Hong Kong and Singapore, the level in the population with hepatitis infection may be as high as 10%.
In the United States, about 20% of patients with chronic hepatitis die of liver failure, and a further 5% develop hepatitis B-associated carcinoma. In the Far East, a large percentage of the population is infected with HBV, and after a long chronic infection (20 to 40 years), approximately 25% of these will develop hepatocellular carcinoma.
After the development of serologic tests for both hepatitis A and B, investigators identified other patients with hepatitis-like symptoms, and with incubation periods and modes of transmission consistent with an infectious disease, but without serologic evidence of hepatitis A or B infection. After almost 15 years, the causative agent was identified as an RNA virus. This virus (designated “hepatitis C”) has no homology with HBV, retroviruses, or other hepatitis viruses.
Hepatitis C (HCV) appears to be the major cause of post-transfusion and sporadic non-A, non-B (NANB) hepatitis worldwide, and plays a major role in the development of chronic liver disease, including hepatocellular carcinoma (Kuo et al., Science 244:362-364, 1989; Choo et al., British Medical Bulletin 46(2): 423-441, 1990). Of the approximately 3 million persons who receive transfusions each year, approximately 150,000 will develop acute hepatitis C (Davis et al., New Eng. J. Med. 321(22): 1501-1506, 1989). In addition, of those that develop acute hepatitis C, at least one-half will develop chronic hepatitis C.
Until recently, no therapy has proven effective for treatment of acute or chronic hepatitis B or C infections, and patients infected with hepatitis must generally allow the disease to run its course. Most anti-viral drugs, such as acyclovir, as well as attempts to bolster the immune system through the use of corticosteroids have proven ineffective (Alter, “Viral hepatitis and liver disease,” Zuckerman (ed.), N.Y.: Alan R. Liss, pp. 537-42, 1988). Some anti-viral activity has been observed with adenosine arabinoside (Jacyna et al., British Med. Bull. 46:368-382, 1990), although toxic side effects which are associated with this drug render such-treatment unacceptable.
One treatment that has provided some benefit for chronic hepatitis B and C infections is the use of recombinant alpha interferon (Davis et al., New Eng. J. Med. 321(22): 1501-1506, 1989; Perrillo et al., New Eng. J. Med. 323:295-301, 1990). However, for patients with hepatitis B infections only about 35% of infectees responded to such treatment, and in perinatal infectees only about 10% responded to treatment. For hepatitis C infections, despite apparent short-term success utilizing such therapy, six months after termination of treatment half of the patients who responded to therapy had relapsed. In addition, a further difficulty with alpha interferon therapy is that the composition frequently has toxic side effects such as nausea, and flu-like symptoms, which require reduced dosages for sensitive patients.
Therefore, there exists a need in the art for therapeutics for treating or preventing disease due to infectious agents such as intracellular bacterial or parasitic infections, or viruses such as hepatitis. The present invention provides such therapeutic agents, and further provides other related advantages.